Methanol (MeOH) is commonly used in the production of crude oil. Methanol is used in deepwater production to prevent the formation of gas hydrates in crude oil exposed to cold temperatures when wells are shut in or when production rates are slowed. In particular, methanol is artificially introduced into the crude oil to prevent the formation of gas hydrates in, for example, deep sea crude production.
The presence of residual methanol in crude oil contaminates the crude oil, which can result in problems in subsequent refining operations when the crude oil is processed. Since methanol is miscible in water, it gets carried with the water in the crude oil to the refinery. The primary impact is on the refinery water treatment systems. When the refinery processes crude oil containing methanol in a desalter, the methanol is removed with the water and sent to the water treatment system where it can drastically upset the balance of the water treatment system. Specifically, when methanol is present, the bacteria that typically breakdowns other components prefers the methanol instead, leaving the other hydrocarbons and toxins untreated. This may produce environmental regulatory issues for the refinery resulting in fines and permit issues. The upset in the balance of the system may also lead to a catastrophic event that renders the water treatment system useless resulting in the need for major remediation efforts. As a result, refineries will typically opt to cut runs of methanol contaminated crude oil instead of risking environmental issues.
The determination of residual methanol content in crude oils is important to safeguard refineries against the processing of the contaminated crude oils that may be detrimental to the refinery causing shutdown of the water treatment plant due to methanol overload. As discussed above, high levels of methanol in the crude oil may jeopardize the refinery's water treatment systems. As such, crude oils with methanol contamination may not be processed in certain refineries. The level of contamination that impacts refining operations, however, may not be the same for all refineries. The equipment and systems at one refinery may be capable of processing crude oils with higher levels of methanol contamination when compared to another refinery. Some refineries have a very low tolerance for methanol contamination.
Currently, ASTM D7059-04 discloses a test method for determining methanol content in crude oil using multidimensional gas chromatography in the range of 15 to 900 ppm of methanol. ASTM D7079 uses gas chromatography with limited sample preparation, but complex hardware requirements. This method as specified by ASTM is only capable of measuring concentrations down to 5 ppm. There is a need for a testing methodology that permits the low-level detection of methanol in crude oil. Low-level methanol detection, for example, 5 ppm of methanol or less may expand a refinery's crude oil selection envelope. This may be especially useful for those refineries with capacity limitations in processing oxygenates containing crude or in discharging effluent water. Furthermore, the detection of low concentrations of methanol may assist refineries to quantifying the impact caused by methanol contamination of crude oil on their systems. As such, the refineries may develop practical guidance on (i) which crude oils are suitable for processing, and (ii) which crude oil should be accepted or rejected, which would allow the most economical deployments of crude across a group of refineries.